Aircraft skis have been manufactured by the present applicant for some years and one particular design shown in printed literature includes a pair of rams each extending from a respective end of the axle of the ground wheel downwardly into engagement with a frame structure of the ski. A lever and torque tube arrangement is arranged so that a lever is connected to each end of the axle and extends to a torque tube connected to the frame structure at a positioned spaced from the axle. The torque tube thus equalizes the movement of the rams so that the ski moves downwardly and upwardly simultaneously on each side of the wheel to prevent twisting or binding of the rams.
The front and rear ends of the ski are tethered by cables which extend from the ski to the aircraft at a suitable location thereon. Each cable includes an elastic section so that the movement of the ski, both from the raising and lowering movement and also from forces due to wind pressure and contact with the ground, are taken up by stretching of the elastic sections.
An alternative arrangement of ski is shown in U.S. Pat. No. 2,977,073 (Ditter) which shows a similar ski arrangement but in this case the ski movement is actuated by a bell crank moved by a ram mounted within the ski body. The ski is tethered by cables which are connected to the actuator mechanism and extend therefrom over pulleys at the front and rear of the ski and from that position to suitable locations on the aircraft. Each of the cables includes an elastic section and is stated to comprise shock cord rigging of a conventional nature. It appears from the drawings, although this is not described, that movement of the ski to the lowered position causes a pay out of the cable connected to the rear part of the ski by an amount to accommodate the downward movement necessary by the rear part of the ski. The description is silent in this matter and the drawings are clearly incorrect since the movement of the ski is insufficient to withdraw the ski to a position above the height of the wheel so that it will still engage the ground when it is not intended to be deployed.
A recently developed aircraft is the Cessna 208 Caravan which has a particularly unusual configuration in that the spacing between wheel and the envelope of the propeller varies fore and aft as well as vertically with wheel loading. This has therefore lead to difficulties in developing a ski for this particular aircraft which will allow the ski to operate effectively in the raised and deployed positions without the possibility of contacting the propeller with the obvious catastrophic results.